Searchlights, also commonly called sky lights, have historically been based on carbon arc or more recently xenon short arc bulbs as the light source. A dense amount of light in a very small area is considered a point source and this coupled with a parabolic mirror allow searchlights to provide an intense projected beam of light. To the present, carbon arcs and xenon short arc lamps have been considered the best existing point sources of light. However, these light sources require large amounts of power, emit large amounts of infrared (IR) and ultraviolet (UV), have a short bulb life, and are not completely stable in their operation. These fixtures use deep parabolic mirrors that reflect the emitted light into a highly collimated beam that under ideal atmospheric conditions appear as tight beams which can be seen for miles.
Several, and usually four, of these fixtures are mounted on a platform which spins and the light's vertical direction is simultaneously tipped up and down. This type of movement projects moving, dancing, sweeping beams of light through the sky, attracting the attention of the public, and drawing them to the source of the beams, in essence an advertising method.
These moving platforms of light require substantial amounts of electricity in order to operate as each light fixture uses between 2,000 and 4,000 watts of electricity. When a group of 4 lights are used and the motors and power supplies are included, the power draw can easily exceed 100 amps and most business either don't have that much excess power or it is not available at the location that the lights must be positioned, such as on a roof. This large power demand requires a generator to also be provided, along with the fuel and an operator, to keep it all fueled and running. It can be a very expensive proposition. A need exists for a searchlight which requires substantially less electricity such that a generator and dedicated operator are not necessary.
There are additional issues such as the bulbs themselves. When they burn out, the service technician must wear protective gear to shield themselves during the re-bulbing process from flying quartz glass as the bulbs, especially when hot, have enormous pressures inside. The bulbs have a life from 200-1000 hours but rarely longer and they can be very expensive depending on their size. The technician usually wears leather wrist covers, a leather chest protector and a face shield over safety goggles whenever he handles one. The bulbs also sometimes explode when being used, destroying not just themselves but a very expensive reflector and the cover glass. Quartz glass shards are nearly invisible when impaled into the human body and consequently are very hard to find often requiring them to be removed by surgeons in a hospital setting. The cover glass in current designs is safety glass and also has UV absorbing properties to protect the public and operator from excessive UV exposure.
The bulb's life decreases and the risk of explosion increases if a careless technician were to accidently touch one with a bare finger wherein the finger oil reacts on the glass when the bulb heats up. The bulbs must also be blasted by a powerful amount of moving cool air and that air exhausted in order to keep the bulbs from melting or exploding. They can do either or both if the fan fails or isn't run long enough after the bulb is turned off such as when a generator unexpectedly fails. These bulbs also suffer from an instable arc which appears as flicker though this is usually just the arc jumping around and not being stable, but the unwanted effect from the defocusing act of this jumping appears to the observer as going on and off rapidly.
The parabolic reflectors used in present searchlights/sky lights are highly reflective mirrors plated onto a nickel metal shape. The process of making these types of mirrors is a long and arduous process using large quantities of nickel, electricity, and vacuum chambers for depositing the nickel to form the highly reflective mirror like surface. This process is well known in the art but the simple fact is that these mirrors are very expensive and their finish is very delicate and easy to damage, even by simple mishandling such as touching them with bare fingers. In the case of searchlights, the reflectors are more complicated in some aspects as they have to be very deep because the light emitted from the xenon bulbs is omni-directional. That is to say that the light comes out at nearly 360 degrees, on all axes, and that light must all then be directed in a single direction with the aid of the reflector.
The reflectors also have to be able to reflect heat and not just the light out of the fixture in the light beam using such technology as in a cold mirror which is mostly made by using specially and expensively applied layers of reflector material in the vacuum chamber process or a traditional hot mirror where the mirror and the nickel absorb a great deal of the heat so it is not transmitted in the light beam. Xenon beams have been known to burn people by the projected IR waves and to start many fires because their beams are so intense. The hot mirrors also have to be cooled by powerful fans in order to remove the intense heat from the fixture.
These reflectors are generally sized by two parameters, total wattage and arc size. The greater the power of the light, the more surface area of mirror is required because a mirror can only absorb or reflect so much IR before it heats up to the point where the surface materials degrade. There is also the issue of point source size vs. focal length. A large source requires a much longer focal length, and the reflector then would require a much larger outside diameter. This increased size exponentially increases the cost of the mold, nickel, and fabrication costs in general so it is best to minimize the point source size to minimize the reflector size requirements. Deep reflectors also cost much more than shallow reflectors but yet they capture a larger angle of emitted light than the shallow versions, a trade-off situation.
The primary function of these searchlights/sky lights is to attract attention and occasionally operators are asked to add colored filters to increase the attention further. The hot light from these arc sources generally fade the filter material in a matter of hours or worse yet melt them beyond usability.
What is needed is new point source light that does not have the requirements of high power usage, short life, does not emit UV, IR, risk explosions, require safety clothing, sensitive handling, powerful cooling fans, deep reflectors, or high cost.